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ABSTRACT Cutaneous and mucocutaneous Candida infections are considered to be important targets for antimicrobial photodynamic therapy (PDT). Clinical application of antimicrobial PDT will require strategies that enhance microbial killing while minimizing damage to host tissue. Increasing the sensitivity of infectious agents to PDT will help achieve this goal. Our previous studies demonstrated that raising the level of oxidative stress in Candida by interfering with fungal respiration increased the efficiency of PDT. Therefore, we sought to identify compounds in clinical use that would augment the oxidative stress caused by PDT by contributing to reactive oxygen species (ROS) formation themselves. Based on the ability of the antifungal miconazole to induce ROS in Candida, we tested several azole antifungals for their ability to augment PDT in vitro. Although miconazole and ketoconazole both stimulated ROS production in Candida albicans, only miconazole enhanced the killing of C. albicans and induced prolonged fungistasis in organisms that survived PDT using the porphyrin TMP-1363 and the phenothiazine methylene blue as photosensitizers. The data suggest that miconazole could be used to increase the efficacy of PDT against C. albicans, and its mechanism of action is likely to be multifactorial. [ABSTRACT FROM AUTHOR]

ABSTRACT Cutaneous and mucocutaneous Candida infections are considered to be important targets for antimicrobial photodynamic therapy (PDT). Clinical application of antimicrobial PDT will require strategies that enhance microbial killing while minimizing damage to host tissue. Increasing the sensitivity of infectious agents to PDT will help achieve this goal. Our previous studies demonstrated that raising the level of oxidative stress in Candida by interfering with fungal respiration increased the efficiency of PDT. Therefore, we sought to identify compounds in clinical use that would augment the oxidative stress caused by PDT by contributing to reactive oxygen species (ROS) formation themselves. Based on the ability of the antifungal miconazole to induce ROS in Candida, we tested several azole antifungals for their ability to augment PDT in vitro. Although miconazole and ketoconazole both stimulated ROS production in Candida albicans, only miconazole enhanced the killing of C. albicans and induced prolonged fungistasis in organisms that survived PDT using the porphyrin TMP-1363 and the phenothiazine methylene blue as photosensitizers. The data suggest that miconazole could be used to increase the efficacy of PDT against C. albicans, and its mechanism of action is likely to be multifactorial. [ABSTRACT FROM AUTHOR]

Mucosal infections caused by the pathogenic fungus Candida are a significant infectious disease problem and are often difficult to eradicate because of the high frequency of resistance to conventional antifungal agents. Photodynamic treatment (PDT) offers an attractive therapeutic alternative. Previous studies demonstrated that filamentous forms and biofilms of Candida albicans were sensitive to PDT using Photofrin as a photosensitizer. However, early stationary phase yeast forms of C. albicans and Candida glabrata were not adversely affected by treatment. We report that the cationic porphyrin photosensitizer meso-tetra ( N-methyl-4-pyridyl) porphine tetra tosylate (TMP-1363) is effective in PDT against yeast forms of C. albicans and C. glabrata. Respiratory-deficient (RD) strains of C. albicans and C. glabrata display a pleiotropic resistance pattern, including resistance to members of the azole family of antifungals, the salivary antimicrobial peptides histatins and other types of toxic stresses. In contrast to this pattern, RD mutants of both C. albicans and C. glabrata were significantly more sensitive to PDT compared to parental strains. These data suggest that intact mitochondrial function may provide a basal level of anti-oxidant defense against PDT-induced phototoxicity in Candida, and reveals pathways of resistance to oxidative stress that can potentially be targeted to increase the efficacy of PDT against this pathogenic fungus. [ABSTRACT FROM AUTHOR]

Meso-tetra-hydroxyphenyl-chlorin (mTHPC, Foscan®), a promising photosensitizer for photodynamic therapy (PDT), is approved in Europe for the palliative treatment of head and neck cancer. Based on work in mice that investigated optimal tumor accumulation, clinical protocols with Foscan® typically employ an interval of 96 h between systemic sensitizer administration and irradiation. However, recent studies in mouse tumor models have demonstrated significantly improved long-term tumor response when irradiation is performed at shorter drug-light intervals of 3 and 6 h. Using a previously published theoretical model of microscopic PDT dosimetry and informed by experimentally determined photophysical properties and intratumor sensitizer concentrations and distributions, we calculated photodynamic dose depositions following mTHPC-PDT for drug-light intervals of 3, 6, 24, and 96 h. Our results demonstrate that the singlet oxygen dose to the tumor volume does not track even qualitatively with tumor responses for these four drug-light intervals. Further, microscopic analysis of simulated singlet oxygen deposition shows that in no case do any subpopulations of tumor cells receive a threshold dose. Indeed, under the conditions of these simulations more than 90% of the tumor volume receives a dose that is approximately 20-fold lower than the threshold dose for mTHPC. Thus, in this evaluation of mTHPC-PDT at various drug-light intervals, any PDT dose metric that is proportional to singlet oxygen creation and/or deposition would fail to predict the tumor response. In situations like this one, other reporters of biological response to therapy would be necessary. [ABSTRACT FROM AUTHOR]

lntracellular calcium concentration ([Ca2+]i) signals are central to the mechanisms underlying fluid and protein secretion in pancreatic and parotid acinar cells. Calcium release was studied in natively buffered cells following focal laser photolysis of caged molecules. Focal photolysis of caged-inositol 1,4,5 trisphosphate (InsP3) in the apical region resulted in Ca2+ release from the apical trigger zone and, after a latent period, the initiation of an apical-to-basal Ca2+ wave. The latency was longer and the wave speed significantly slower in pancreatic compared with parotid cells. Focal photolysis in basal regions evoked only limited Ca2+ release at the photolysis site and never resulted in a propagating wave. Instead, an apical-to-basal wave was initiated following a latent period. Again, the latent period was significantly longer under all conditions in pancreas than parotid. Although slower in pancreas than parotid, once initiated, the apical-to-basal wave speed was constant in a particular cell type. Photo release of caged-Ca2+ failed to evoke a propagating Ca2+ wave in either cell type. However, the kinetics of the Ca2+ signal evoked following photolysis of caged-InsP3 were significantly dampened by ryanodine in parotid but not pancreas, indicating a more prominent functional role for ryanodine receptor (RyR) following InsP3 receptor (InsP3R) activation. These data suggest that differing expression levels of InsP3R, RyR, and possibly cellular buffering capacity may contribute to the fast kinetics of Ca2+ signals in parotid compared with pancreas. These properties may represent a specialization of the cell type to effectively stimulate Ca2+-dependent effectors important for the differing primary physiological role of each gland. [ABSTRACT FROM AUTHOR]

Phthalocyanine 4 (Pc 4) is a promising photosensitizer currently in clinical trials. Photobiological responses to Pc 4 photodynamic therapy (Pc 4-PDT) have been characterized extensively, but relatively little has been done to evaluate dose metrics for this sensitizer. We describe an irradiation-induced increase in fluorescence in tumor cell monolayers. This increase is due solely to enhanced fluorescence from Pc 4, as confirmed by confocal spectroscopy. In EMT6 cells incubated with 250 n M Pc 4 for 24 h, the maximum increase in fluorescence is approximately 3.7-fold above baseline levels. This increase occurs over a range of fluences, 0.05 – 0.6 J cm−2, where clonogenic survival decreases by 3 orders of magnitude. Light scattering measurements performed on similarly treated EMT6 cells in suspension suggested a Pc 4-PDT-mediated mitochondrial swelling of approximately 13% at 0.6 J cm−2, where fluorescence enhancement saturates under these treatment conditions. Fluorescence imaging and light scattering experiments performed at a five-fold lower Pc 4 incubation concentration revealed a reduced fluorescence enhancement at a five-fold higher fluence, which produced comparable mitochondrial swelling. Taken together, these data suggest that Pc 4 is initially aggregated at high local concentration in mitochondria and that irradiation relaxes the quenching of Pc 4 fluorescence through a mechanism that may involve mitochondrial swelling. [ABSTRACT FROM AUTHOR]

We have developed a comprehensive theoretical model for rigorously describing the spatial and temporal dynamics of oxygen (3O2) consumption and transport and microscopic photodynamic dose deposition during photodynamic therapy (PDT) in vivo. Previously published models have been improved by considering perfused vessels as a time-dependent 3O2 source and linking the 3O2 concentration in the vessel to that within the tissue through the Hill equation. The time-dependent photochemical 3O2 consumption rate incorporates sensitizer photobleaching effects and an experimentally determined initially nonuniform photosensitizer distribution. The axial transport of 3O2 is provided for in the capillaries and in the surrounding tissue. A self-sensitized singlet oxygen (1O2)-mediated bleaching mechanism and the measured, initially nonuniform distribution of meso-tetrahydroxyphenyl chlorin at 3 h after intravascular administration were used to demonstrate the capabilities of the model. Time-evolved distributions of 3O2 concentration were obtained by numerically solving two-dimensional diffusion-with-reaction equations both in the capillary and the adjacent tissue. Using experimentally established physiological and photophysical parameters, the mathematical model allows computation of the dynamic variation of hemoglobin-3O2 saturation (SO2) within the vessels, irreversible sensitizer degradation due to photobleaching, and the microscopic distributions of 3O2, sensitizer concentration, and 1O2 dose deposition under various irradiation conditions. The simulations reveal severe axial gradients in 3O2 and in photodynamic dose deposition in response to a wide range of clinically relevant treatment parameters. Thus, unlike former Krogh cylinder-based models, which assume a constant 3O2 concentration at the vessel, this new model identifies conditions in which 3O2 depletion and minimal deposition of reacting 1O2 exist near the end of axial segments of vessels and shows that treatment-limiting 3O2 depletion is induced at fluence rates as low as 10 mW cm-2. These calculations also demonstrate that intercapillary heterogeneity of photosensitizer contributes significantly to the distribution of photodynamic dose. This more rigorous mathematical model enables comparison with experimentally observable, volume-averaged quantities such as SO2 and the loss of sensitizer fluorescence through bleaching that have not been included in previous analyses. Further, it establishes some of the intrinsic limitations of such measurements. Specifically, our simulations demonstrate that tissue measurements of SO2 and of photobleaching are necessarily insensitive to microscopic heterogeneity of photodynamic dose deposition and are sensitive to intercapillary spacing. Because prior knowledge of intercapillary distances in tumors is generally unavailable, these measurements must be interpreted with caution. We anticipate that this model will make useful dosimetry predictions that should inform optimal treatment conditions and improve current clinical protocols. [ABSTRACT FROM AUTHOR]

A correction to the article "A comprehensive mathematical model of microscopic dose deposition in photodynamic therapy" that was published in the 2007 issue is presented.

During drug development, tissue samples serve as indicators of disease activity and pharmacodynamic responses. Reliable non-invasive measures of drug target engagement will facilitate identification of promising new treatments. Here we develop and validate a novel bi-transgenic mouse model of myotonic dystrophy type 1 (DM1) in which expression of either DsRed or GFP is determined by alternative splicing of an upstream minigene that is mis-regulated in DM1. Using a novel in vivo fluorescence spectroscopy system, we show that quantitation of the DsRed/GFP ratio provides an accurate estimation of splicing outcomes in muscle tissue of live mice that nearly doubles throughput over conventional fluorescence imaging techniques. Serial in vivo spectroscopy measurements in mice treated with a C16 fatty acid ligand conjugated antisense (LICA) oligonucleotide reveal a dose-dependent therapeutic response within seven days, confirm a several-week duration of action, and demonstrate a two-fold greater target engagement as compared to the unconjugated parent oligonucleotide. Myotonic dystrophy type 1 (DM1) is associated with aberrant transcript splicing. Here, the authors develop a transgenic mouse model expressing a bi-chromatic reporter system that allows non-invasive monitoring of splicing of a transcript altered in DM1 in vivo, and show that it allows for evaluation of the therapeutic response to treatment with antisense oligonucleotides. [ABSTRACT FROM AUTHOR]

Genetically-encoded photosensitizers produce reactive oxygen species (ROS) in response to light. Transgenic expression of fusion proteins can target the photosensitizers to specific cell regions and permit the spatial and temporal control of ROS production. These ROS-generating proteins (RGPs) are widely used for cell ablation, mutagenesis and chromophore-assisted light inactivation of target proteins. However, the species produced by RGPs are unclear due to indirect measures with confounding interpretations. Recently, the RGP mini “Singlet Oxygen Generator” (miniSOG) was engineered from Arabidopsis thaliana phototropin 2. While miniSOG produces singlet oxygen ( 1 O 2 ), the contribution of superoxide (O 2 • - ) to miniSOG-generated ROS remains unclear. We measured the light-dependent O 2 • - production of purified miniSOG using HPLC separation of dihydroethidium (DHE) oxidation products. We demonstrate that DHE is insensitive to 1 O 2 and establish that DHE is a suitable indicator to measure O 2 • - production in a system that produces both 1 O 2 and O 2 • - . We report that miniSOG produces both 1 O 2 and O 2 • - , as can its free chromophore, flavin mononucleotide. miniSOG produced O 2 • - at a rate of ~4.0 µmol O 2 • - /min/µmol photosensitizer for an excitation fluence rate of 5.9 mW/mm 2 at 470 ± 20 nm, and the rate remained consistent across fluences (light doses). Overall, the contribution of O 2 • - to miniSOG phenotypes should be considered. [ABSTRACT FROM AUTHOR]